In general, integrated circuit (IC) devices manufactured today rely upon an elaborate system of conductive interconnects for wiring together transistors, resistors, and other IC components which are formed on a semiconductor substrate. The technology for forming these interconnects is highly sophisticated and well understood by practitioners skilled in the art. In a typical IC device manufacturing process, many layers of interconnects are formed over a semiconductor substrate, each layer being electrically insulated from adjacent layers by an interposing dielectric layer. It is important that the surface of these interposing dielectric layers be as flat, or planar, as possible to avoid problems associated with optical imaging and step coverage which could frustrate the proper formation and performance of the interconnects.
As a result, many planarization technologies have evolved to support the IC device manufacturing industry. One such technology is called chemical mechanical polishing or planarization (CMP). CMP includes the use of lapping machines and other chemical mechanical planarization processes to smooth the surface of a layer, such as a dielectric layer, to form a planar surface. This is achieved by rubbing the surface with an abrasive material, such as polishing pad, to physically etch away rough features of the surface. Rubbing of the surface may be performed in the presence of certain chemicals which may be capable of chemically etching the surface as well. After a dielectric layer has been sufficiently smoothed using CMP, interconnects may be accurately and reliably formed on the resulting planar surface.
When a wiring pattern is formed on a wafer and then an insulating layer is formed over the entire surface, the insulating layer may have protrusions (surface topography), because some areas are located over the wiring pattern and the other areas are not located over the wiring pattern. In the polishing process of the insulating layer, the protrusions of the insulating layer are flattened uniformly. In this process, it is required that a polishing pad conforms to deflections (global waviness) of the wafer and polishe local topographies on the wafer well to flatten the surface of the wafer uniformly.
For example, when a soft polishing pad is used, the pad conforms even to the local topographies of the insulating layer, because the polishing pad itself elastically deforms. As a result, the polishing pad polishes not only projected portions but also depressed portions as well. This means that it is difficult to flatten local topographies on the insulating layer.
On the other hand, when a rigid polishing pad is used, the pad tends to polish only the projected portions in the global deflection of the wafer, but not polish the local topographies uniformly. As a result, it is difficult to polish the insulating layer uniformly in a global range.
Accordingly, in order that the polishing pad conforms to the deflections (global waviness) of the wafer and flattens the local topographies well, a variety of improved polishing apparatuses have been proposed. For example, in U.S. Pat. No. 5,212,910, an improved polishing apparatus is described. The apparatus includes a first layer, a second layer and a third layer. The first layer is made of an elastic material such as spongy rubber or foam rubber, and is attached to a turn table. The second layer is made of a rigid material such as epoxy, segmented into individual sections by grooves. The second layer is attached to the first layer. The third layer is made of a porous material having a good slurry-transportability, such as Rodel SUBA500 (Product No.). The third layer is in contact with the silicon wafer to polish.
In the conventional apparatus, each segmented section of the rigid material (the second layer) moves vertically while being cushioned by the elastic material of the first layer, so that the polishing pad (third layer) can conform to the global deflections of the wafer surface. Each segmented section of the second layer is not deformed, so that the polishing pad is flatly in touch with the local protrusions on the wafer. As a result, the polishing pad conforms to the global deflections of the wafer, and at the same time, well polishes the local protrusions.
In such a polishing apparatus, the polishing pad can be attached to the turn table with two different ways (techniques). According to one technique, the whole surface of the polishing pad is adhesive-bonded to the turn table, which is hereinafter called "adhesive-bonding technique." According to the other technique, the polishing pad is stretched with a predetermined tension and is held on to the turn table without adhesive bonding, which is hereinafter called "stretch-holding technique."
According to the adhesively-bonding technique, some air bubbles may get into a space between the turn table and the polishing pad during the attachment process of the polishing pad, because the polishing pad is adhesively-bonded to the turn table, for example with a double-sided tape. If air bubbles get into the space, the polishing pad is locally protruded. The polishing rate at the protruded portion becomes larger locally, therefore, the wafer is not polished uniformly. For that reason, the attachment accuracy varies depending on the operator who installs the polishing pad, therefore, it is required to attach the polishing pad to the turn table by an experienced operator.
In general, the polishing pad is frequently changed to new one, therefore, the attachment accuracy of the polishing pad is not stable, and it is difficult to perform a polishing process accurately. As a result, the polishing apparatus itself does not always work well, and the operating efficiency of the apparatus is decreased. Further, when the polishing pad is removed from the turn table, some small pieces of the double-sided tape may remain on the turn table. It is required to remove all the remains.
On the other hand, when the polishing pad is attached to the turn table by the stretch-holding technique, air bubbles do not easily get into the space between the polishing pad and the turn table. Even though, some air bubbles get into the space, those are easily taken out. Therefore, the polishing pad can be easily attached to the turn table by an inexperienced operator. The polishing quality is maintained high, because the attachment accuracy of the polishing pad is stable independently from the operator who attaches the polishing pad. Accordingly, the polishing pad conforms to the global deflections of the wafer, and at the same time, well polishes the local protrusions on the wafer.
In Japanese Laying Open Kokai No. H5-285825, a polishing apparatus includes an elastic member between a turn table and a polishing pad. The polishing pad is attached to the turn table by the stretch-holding technique. In this apparatus, the elastic member is arranged between the polishing pad and the turn table, so that the polishing pad conforms to global deflections of the wafer. The polishing pad is made of rigid material, so that local protrusions on the wafer are polished and flattened well. The polishing pad is attached to the turn table by the stretch-holding technique, so that the apparatus has no disadvantages caused by the adhesively-bonding technique.
In this apparatus, the polishing pad is not bonded to the elastic member, but is held with a predetermined tension. The polishing pad is made of a material which is rigid and well holds a polishing slurry. The material, which holds the polishing slurry well, may be of foamed material having a high degree of swelling, so that the polishing pad is swelled and deformed when absorbing the polishing slurry. When the polishing pad is swelled, the attachment between the polishing pad and the turn table gets loose.
Further, when the polishing process is repeated many times, shear stress makes wrinkles in the shear direction (direction in which the polishing pad and the flat plate object are rubbed) on the polishing pad. When the wrinkles are made on the polishing pad, a part of the wafer is locally over polished, so that the entire surface of the wafer is not polished uniformly. Especially in an apparatus that performs a dressing process of a polishing pad, the polishing pad is locally over dressed at portions where the wrinkles formed, so that the entire surface of the wafer is not polished uniformly. In other words, specific regions of the polishing pad are locally over shaved, therefore, the polishing pad can not be used over a long period of time.